1. Field of the Invention
The present disclosure relates to an iontophoresis device for administering positively charged drug ions to a living body by an action of a positive electrical potential applied to an active electrode structure holding the drug ions.
2. Description of the Related Art
An iontophoresis device generally includes an active electrode structure holding a drug solution whose active ingredient is dissociated to positive or negative ions (drug ions) and a counter electrode structure that functions as a counter electrode of the active electrode structure. The drug ions are administered to a living body by the application of an electrical potential or voltage with the same polarity as that of the drug ions to the active electrode structure under the condition that both the assemblies are in contact with a biological interface (e.g., skin, mucus membrane) of the living body (e.g., human being or animal).
The charge supplied to the active electrode structure is consumed by the movement of the drug ions to the living body and the release of biological counter ions present in the living body and having a polarity opposite to that of the drug ions) to the active electrode structure. The biological counter ions typically released are those having a small molecular weight (e.g., Na+ and Cl−) and hence high mobility. Therefore, the transport number (i.e., ratio of the amount of current contributing to the movement of the drug ions among the whole current supplied to the active electrode structure) decreases, which makes it difficult or impossible to administer a sufficient amount of drug.
JP 3030517 B, JP 2000-229128 A, JP 2000-229129 A, JP 2000-237326 A, JP 2000-237327 A, JP 2000-237328 A, JP 2000-237329 A, JP 2000-288097 A, JP 2000-288098 A and WO 03/037425 disclose iontophoresis devices that attempt to solve the above-mentioned problem.
More specifically, in each of the iontophoresis devices described in the above-cited references, an active electrode structure is composed of an electrode, a drug holding part placed on a front side (i.e., a side facing to the biological interface when in use) of the electrode, and an ion-exchange membrane that is placed on a front side of the drug holding part and selectively passes ions with the same polarity as that of the drug ions held by the drug holding part, and the drug ions are administered through the ion-exchange membrane, whereby the release of biological counter ions is suppressed in an effort to enhance the transport number and thus the administration efficiency of the drug.
In the iontophoresis devices in the above-cited references, the active electrode structure further includes an electrolyte solution holding part for holding an electrolyte solution in contact with the electrode, and an ion-exchange membrane that is placed on a front side of the electrolyte solution holding part that selectively passes ions having a polarity opposite to that of the polarity of the drug ions, and the drug holding part is placed on a front side of the ion-exchange membrane, in an effort to prevent the drug ions from being decomposed, by isolating the drug ions from the electrode and preventing the movement of H+ or OH− ions generated at the electrode to the drug holding part and the biological interface of a living body.
Furthermore, JP 2004-188188 A discloses a purported improvement over the iontophoresis devices disclosed in JP 3030517 B, JP 2000-229128 A, JP 2000-229129 A, JP 2000-237326 A, JP 2000-237327 A, JP 2000-237328 A, JP 2000-237329 A, JP 2000-288097 A, JP 2000-288098 A and WO 03/037425. JP 2004-188188 A teaches that the administration amount of a drug can be enhanced remarkably by using an ion-exchange membrane in which a porous film composed of a material such as polyolefin, vinyl chloride resin, or fluorine resin is filled with an ion-exchange resin (a resin providing an ion-exchange function).
As described above, the iontophoresis device disclosed in JP 2004-188188 A is purported to be the one having the most excellent administration efficiency of a drug among those which are known at present. However, further improvements with respect to administration efficiency of drug delivery are desirable, even as compared with the iontophoresis device disclosed in JP 2004-188188 A.